The present invention refers to a method of correcting physically conditioned errors in the measurement of an object, and especially to a method of correcting physically conditioned errors in the measurement of the width of microscopic objects whose dimensions are of the same order of magnitude as the wavelength of the illumination source.
The further development in the field of semiconductor technology leads to ever finer chip structures and this entails increasing circuit complexity. In addition to problems in the production of such structures, problems also arise in the examination of such structures, viz. when the structures produced are imaged for checking them, e.g. by measuring the width thereof. An example for a conventional method is the measurement of structure widths making use of optical microscopes, the object to be measured being illuminated in transmitted light or incident light and the resultant intensity image being subsequently observed and measured.
These methods are disadvantageous insofar as the intensity image is composed of superpositions originating from the structure to be measured as well as from structures which are arranged in the vicinity of the structure to be measured. It follows that the intensity image of the structure to be measured and therefore the measurement result are directly influenced and corrupted by the surroundings of the object to be measured. This phenomenon is known under the name of xe2x80x9cproximity effectxe2x80x9d. Due to the corruption of the intensity images, it is impossible to make any reliable statements with regard to the shape and the dimensions of the structures produced and therefore the reliability of the production process, when the width of the object is measured.
It is the object of the present invention to provide a method of correcting physical errors in the measurement of an object so that measurement errors originating from influences of neighbouring structures are avoided.
A method of correcting physically conditioned errors in the measurement of an object, includes
(a) detecting an image of the object to be measured;
(b) measuring the object imaged in the detected image;
(c) determining a measurement error caused by structures which are arranged in the vicinity of the object to be measured; and
(d) correcting the measurement of step (b) in dependence on the measurement error determined.
The present invention is based on the finding that the corruption of the intensity image and the resultant effect on the measurement resultxe2x80x94the corruption being produced by the surroundings of an object to be measured when this object is being irradiated or illuminatedxe2x80x94can be corrected by correcting the image of the object to be measured with due regard to the error contributions from the object surroundings. Starting from the image produced in this way, the influence of the structural surroundings or object surroundings on the measurement result is eliminated. The measurement result corrected in this way will then correspond to the actual physical dimensions of the object to be measured.
According to one aspect a correction method is provided in the case of which, starting from the image produced, an intensity image of the object to be measured and of its surroundings is detected, whereupon a correction value is determined from the global image especially for the structure to be measured, the correction value depending on structures which are arranged in the vicinity of the object to be measured. Finally, the intensity image is measured and corrected in dependence on the value determined. The result of this measurement is then always a measurement value which has undergone correction and which therefore approaches the actual magnitude of the object to be measured more closely.
According to a further aspect, the detected image or intensity image contains the object to be measured and the structural surroundings thereof, so that, when the correction value or correction values is/are being determined, the measurement errors are determined and corrected in dependence on the structural surroundings contained in the intensity image detected.
According to a further aspect, the detected image or intensity image contains the object to be measured and the relevant surroundings thereof, which have an influence on the correction value to be calculated. Furthermore, a layout description of the object to be measured and imaged, respectively, and of the structural surroundings thereof is provided, and the correction factor for the measurement result is determined only in dependence on the layout description provided.
According to a further aspect, the microscopic object imaged as an image or intensity image is measured and the actual intensity image is approximated to the ideal conditions by means of a correction function.
In addition to a light source, also other radiation sources, such as an electron beam source or an X-ray source, are suitable to be used as an irradiation source.